Modern video-imaging systems use high brightness lamps to transmit an image either through, or reflected from, a small digital pixelation device. As used herein, a “digital pixelation device” (“DPD”) can comprise many small mirrors, a liquid crystal display (LCD), or one of many other concepts being developed for video-imaging devices. For instance, Texas Instruments, of Dallas, Tex., has developed digital light processing (DLP), which is an example of a DPD. The lamps used to drive a DPD are often ultra-high pressure (UHP) mercury lamps, chosen for their white color spectrum and high brightness. The optics used to collect the light consist exclusively of imaging optics, that is, of reflectors made of one, or several, elliptical or parabolic reflectors.
Imaging optics have disadvantages in that (1) they are inherently inefficient, (2) they preserve artifacts of the light source (such as very bright or very dim regions), and (3) they are large and often need a long air gap between the light source and the digital pixelation device.
Further, the angular distribution of light in the foregoing video projection systems is very important. Too broad a spread will result in light “bleeding” through from pixel to pixel, which affects the overall quality of the picture—especially in dark sections. Too narrow a distribution can be a problem when it is desired to make the image viewable at wide angles to the screen. Systems using non-imaging optics can be designed to substantially match the angular distribution of light needed. For instance, to supply light below 15 degrees to a HDTV DLP, 1.5″ diagonally and 16:9 aspect ratio, the lamp diameter would be 7.3 mm. Metal Halide lamps of this size, which are capable of operation in the presence of oxygen, are currently available.
It would be desirable to provide an illumination system for video-imaging devices based on non-imaging optics, which is highly efficient and very compact compared to systems based on imaging optics, without sacrificing, or even improving, quality.
It would also be desirable to provide an illumination system for video-imaging devices based on non-imaging optics, which can eliminate some of the components required for illumination systems based on imaging optics.